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Heat transfer

Heat, a form of kinetic energy, is transferred in three ways: conduction, convection, and radiation. Heat transfer (also calledthermal transfer) can occur only if a temperature difference exists, and then only in the direction of decreasing temperature.Beyond this, the mechanisms and laws governing each of these ways are quite different.
Heat transfer determines or accompanies many processes in daily life, in technology, and in nature—for example,meteorological processes at the earth’s surface and the evolution of stars and planets. In many cases, such as in the studyof dehydration, evaporative cooling, and diffusion, heat transfer is considered together with mass transfer. A special case ofheat transfer is the flow of heat from one heat-transfer fluid to another through a solid wall separating the fluids or through aninterface between the fluids.

Rate of Heat transfer

The rate at which heat is transferred or conducted through a substance is directly proportional to the

1 . Area of the surface (A) perpendicular to the flow of heat and

2. The temperature gradient ΔTxΔTx along the path of heat transfer

For a one dimensional steady state heat transfer Rate of Heat Transfer is expressed by Fourier equation:

Q =kAΔT / Δx

where,

K = Thermal Conductivity depends on the material

A = Area of the surface

ΔT / Δx = Temperature gradient for small change in temperature with respect to distance.

Types of Heat transfer

There are three modes of Heat transfer:

        1. Conduction
        2. Convection
        3. Radiation
  • Conduction is when heat flows through a heated solid through a heat current moving through the material.
  • Convection is when heated particles transfer heat to another substance, such as cooking something in boiling water.
  • Radiation is when heat is transferred through electromagnetic waves, such as from the sun. Radiation can transfer heat through empty space, while the other two methods require some form of matter-on-matter contact for the transfer.